JK Rowling says she has begun work compiling her long-awaited encyclopedia of the Harry Potter world.

In the 'frequently asked questions' section on her new author website, Rowling said that "for a long time I have been promising an encyclopedia of Harry's world, and I have started work on this now – some of it forms the new content in Pottermore. It is likely to be a time-consuming job, but when finished I shall donate all royalties to charity."

In 2008, Rowling took independent American publisher RDR Books to court over its plans to publish the Harry Potter Lexicon, an unauthorised A to Z of the Potter stories. Rowling described the book as "wholesale theft of 17 years of my hard work", and won the case.

The announcement about the encyclopedia, on the day website Pottermore opened to all comers, follow last week's news that she will publish adult novel The Casual Vacancythis autumn.